1. Field of the Invention (Technical Field)
The present invention relates to battery charging control methods and apparatuses.
2. Background Art
Note that the following discussion refers to a number of publications by author(s) and year of publication, and that due to recent publication dates certain publications are not to be considered as prior art vis-a-vis the present invention. Discussion of such publications herein is given for more complete background and is not to be construed as an admission that such publications are prior art for patentability determination purposes.
In the last decade, the development of electric and hybrid vehicles and the rapid expansion of portable computers, electronic devices and telecommunication tools in the U.S. and other regions of the world have sparked an enormous interest in developing advanced battery systems and sprawling a strong demand in high power applications. These developments called for rapid prototyping of the batteries and devices and better charging and safety control and cycle life. Charging technology becomes an indispensable part of the battery technology development, particularly for safety, reliability, and cycle life considerations.
Electric and hybrid vehicles (EHVs) promise much reduced emissions, high fuel economy, and lowered maintenance costs. However, the high power and sporadic usage of the battery pack and the effects from such usage on battery performance remain a great concern for automakers and have a direct impact on consumers"" acceptance. As for pure electric, an additional demand for reliable, high-power, rapid charging infrastructure is embracing. Similar situations are emerging in the computer, mobile telecommunication, and network infrastructure, where demands for reliable power, steady performance and rapid charging capability are challenges need solutions.
Among all battery charging techniques used to date the most prevailing charge controls for the Nixe2x80x94Cd and Nixe2x80x94MH batteries, for example, are often based on temperature acceleration (xcex94T/xcex94t) and peak voltage detection. Recently, we proposed a new charge technique for the Nixe2x80x94MH traction batteries by detecting the internal pressure built-up [Yang, X. G. and B. Y. Liaw, xe2x80x9cFast Charging Nickel-Metal Hydride Traction Batteries,xe2x80x9d J. Power Sources, 101, 158 (2001)]. The pressure-control-based charge technique is more sensitive and reliable than the conventional temperature or/and voltage detection approaches because of the direct monitoring of the gas evolution and recombination. The disadvantage of the temperature detection comes from the inherent large heat capacity of the battery that makes the detectable temperature acceleration insensitive until the battery is substantially overcharged with severe gassing. Another problem is the ambient temperature change that could easily skewed the temperature detection, making the charging control vulnerable. Repeated overcharging is hazardous to battery cycle life. On the other hand, the peak voltage determination for full charge is hindered by aging and inhomogeneous electrode reaction. Both deficiencies could cause local overcharge, dry-out and shortened battery life.
The present invention comprises methodologies that can be used in battery charging control. The invention comprises methods of utilizing a pressure probe, measuring and monitoring the pressure change inside a battery, interpretation of the pressure profile and its change, using the interpretation of such changes as the primary protocols in conjunction with other parameters monitored and determined in the process in the termination of the battery charging process.
The invention also comprises battery charge control protocols that use internal battery gas pressure and its change in a charging process. The pressure-based protocols can be as simple as a pressure lid or as complicated as a dependence on its change with various combinations of time, operating temperature range, the ambient pressure in the operating environment, voltage range and/or its change, current level and/or its change, charge inputs and/or outputs, and other possible pertinent parameters (such as age, state of charge, or state of health, etc.) that are also monitored or determined in the charging process or control algorithm.
The invention further comprises battery charging control protocols that can be used in battery chemistries that have side reactions that generate gas species, therefore create pressure in the battery in such a way that the gas pressure change can be interpreted to predict the degree of the reaction, the reaction rate, the extent of the impacts on the battery performance, and the possible effects that can degrade the battery performance including life. The pressure-based control protocols can prevent gas generating side reactions to degrade battery performance or its life.
The invention additionally comprises battery charging control protocols that can be used in batteries that use aqueous electrolytes and organic electrolytes that involve either gas reactions or gas generating side reactions. Without proper control of the pressure changes in the battery, the battery will not perform efficiently or effectively. The pressure control provides the most direct monitoring of the chemistry involved in the battery, thus is capable of minimizing side reactions that generate gas species and cause adverse effects to the battery performance.
The invention still further comprises the pressure controlled charge protocols that can be used in nickel-based chemistries and batteries effectively with high charge efficiency at high power or high rate charging and can deliver reliable capacity consistently. The charging rate can be as high as more than 3C rate without signs of degradation from high rate charging.
The invention yet further comprises battery charging control protocols that use pressure-based control strategy to protect the battery from degradation caused by gas generating reactions. The gas generation could occur depending on operating temperature, working voltage range, current level, charge inputs, impurities and contaminants, and other circumstantial conditions that can change the reaction chemistry to produce gas species.
The invention also comprises battery charging protocols that can take the advantages of battery design, configuration, and modification of the chemistry to withstand high pressure excursions and exhibit better mechanical limits to sustain pressure changes without compromising or degrading battery performance. The pressure limits of the operation could be decided by the mechanical integrity of the containment and its tolerance to the pressure change. The higher the pressure limits, the better the charge return and the higher the availability of the capacity.
The invention additionally comprises battery charging protocols that use pressure control to minimize thermal excursion or temperature change to improve charge efficiency, operating safety and reliability of power delivery.
The invention further comprises the use of pressure probing devices to monitor the gas pressure change in a battery, the method of providing secured seal of the battery containment and access to the headspace for pressure measurement and monitoring, and the feedback of the pressure signals to the charge control mechanism so proper termination of the charging process can be executed with a;proper algorithm. The invention comprises the intelligence of using and interpreting the pressure profiles and their behaviors as a major factor in determining the termination conditions for the battery charging process.
The invention yet further comprises the design, deployment, installation, implementation of gas sensing devices and pressure probes in the control of battery charging process. The design, deployment, installation and implementation of the charge control strategies and protocols include but not limit to hardware and physical devices and software development, algorithm implementation, and signals and commands communication.
The invention of using the pressure-controlled protocols is more effective in controlling charging processes in nickel-based aqueous battery chemistries, such as Nixe2x80x94Cd and Nixe2x80x94MH. For any battery chemistry, the higher the pressure excursion, the better the sensitivity in the control. The higher the charge rate, or the higher the charge power level, the more effective the protocols can serve than the other conventional techniques based on temperature or voltage measurements.
A primary object of the present invention is to develop a reliable protocol to properly terminate the battery charging process, enhance charging efficiency and protect or even improve battery life.
A primary advantage of the present invention is that pressure-based battery charging control and algorithms can achieve the above objectives and goals better than the conventional voltage and/or temperature-based techniques. The control is also much simpler than the conventional techniques that track voltage, temperature, and/or amp-hour charge inputs, therefore potentially more cost effective.
Other objects, advantages and novel features, and further scope of applicability of the present invention will be set forth in part in the detailed description to follow.